1. Field of the Invention
The present invention relates to an x-y plotter, and more particularly, it relates to an x-y plotter having an increased drawing speed and a reduced noise level.
2. Description of the Related Arts
With the growing use of personal computers, users want to display information processed by the computer as a picture, even in domestic use, and accordingly, there has long been a need for the realization of an inexpensive x-y plotter having a high efficiency (high speed, low noise, etc.).
Generally, an x-y plotter comprises a carriage which carries a writing pen and which is moved right and left (x-directions) by a motor through a drive belt, to draw a letter or a picture on a recording paper moved forward and backward (y-directions) perpendicularly to the x-directions, by a motor. The writing pen is supported in the carriage so as to be able to move upwardly and downwardly between an inoperative position, i.e., an upward position in which the pen is separated from the recording paper, and an operative position, i.e., a downward position (writing position) in which the pen comes into contact with the recording paper to draw a picture, etc. Namely, in the operative position, the pen and the paper are moved in the x-directions and the y-directions normal thereto, respectively, so that a desired two-dimensional picture or letter can be drawn on the paper.
The recording paper is held on a table (plate) by and between pinch rollers and friction rollers opposed thereto, so that the paper can be moved in the y-directions on the table in accordance with the rotation of the friction rollers, which are in turn driven by the motor.
A plurality of writing pens are stored in a rotatable pen holder, from which a desired pen is automatically and selectively taken by the carriage.
In the prior art, however, the recording paper may be partially separated from the table, especially when the paper is moved in the y-directions at a high speed. In particular, if the partial separation of the recording paper from the table takes place in the vicinity of the writing pen, the writing pen can be accidentally brought into contact with the recording paper even when the writing pen is in the inoperative position, i.e., in the upward position, and as a result of this undesirable contact of the recording paper with the writing pen, an unnecessary line or figure is drawn on the recording paper during the relative movement of the writing pen and the recording paper. To avoid the accidental contact of the recording paper with the writing pen, even if the paper is partially separated from the table, the displacement of the upward and downward movement of the writing pen must be increased, resulting in an increase of the time necessary for the upward and downward movement of the writing pen, and thus a higher drawing speed cannot be obtained.
Furthermore, since the paper is moved on the table while a substantial part of the recording paper is in slide-contact therewith, a relatively loud noise is caused due to the frictional surface contact between the recording paper and the table.
In the prior art, the presence and absence of a desired writing pen in the pen holder and on the carriage are optically detected by a transmission type photosensor or a reflection type photosensor. The transmission type photosensor has a light emitter and a light receiver opposed thereto, so that light emitted from the light emitter can be detected by the light receiver to detect the absence or presence of the pen in the pen holder or on the carriage. Similarly, the reflection type photosensor has a light emitter and a light receiver located on the same side of the pen holder or the carriage, so that light emitted from the light emitter and reflected from the object, i.e., the writing pen, can be detected by the light receiver to detect the absence or presence of the writing pen.
In this detecting mechanism of the prior art, however, a writing pen having a black body can not be detected by the reflection type photosensor, since the light is absorbed, and conversely, in a pen which has a transparent body whereby the contents therein are made visible, ink contained in the transparent body can not be detected by the transmission type photosensor, since the light is transmitted through the transparent body of the pen without detecting the presence thereof.